Engine signal apparatus



sePt- 3, 1946. j E. CHANDLER 2,407,134

ENGINE SIGNAL APPARATUS F'ledug. lll, 1945 3 Sheets-Sheet 1 u, N fr) n C9 m A r'- f 9. 3 3^@ S, il m l P mi m s n N :2 g F 2' 4N i I. i

m g s y INVENTOR. U\ MIEVONECHANDLER AGE NT Sept. 3, 19,46. M. E'. CHANDLER 2,407,134

ENGINE "SIGNAL APPARATUS Filed Aug. 1l, 1943 3 Sheets-Sheet 2 AGENT sept. 3, 1946. M E, CHANDLER 2,407,134

ENGINE SIGNAL APPARATUS Filed Aug. 11, 1945 5 sheets-sheet :s

1,72 y mms/roza AGENT Patented Sept. 3, 1946 to Chandler-Evans Corporation, `South Meriden, Conn., a corporation of Delaware Application A ugust 11, 1943", serial No. 498,138'

The present invention relates to safety signal" apparatus for use on aircraft, and particularly to signal apparatus for indicating to the pilot of an aircraft that the mixture of fuel and air being supplied to an engine of the aircraft isof improper proportions.`

On most modern aircraft, a control lever is pro'- vided by which the `pilot may determine Whether the carburetor is to supply the engine with a rich fuel and air mixture, or a lean mixture. It is desirablefor reasons of economy to operate with a lean mixture under most flight conditions. However, if the engine is operated with a lean mix` ture under conditions of high power requirements, it may overheat. Furthermore, it may not pro'- duce the required power. Therefore a control lever is provided by whichthe pilot may cause the engine to be supplied with a rich mixture under such conditions as take off or climbing', while he may select alean mixture for normal or cruising flight.

It has been found that pilots sometimes forget to operate this lever at the proper time. Since (ci. 17T-311) the lever is usually moved to the'rich position for take olf, it maybe left at that position for a considerable time after the plane has reached its cruising altitude. consumption, and may result in .the planes fuel supply running low before its destination isV reached, with consequent necessity of a forced landing. Where a landv plane is operated over This results in excessive fuel water, for example, the plane and all its occu` Y pants may be lost merely because the pilot forgot to restore the mixture control lever to the lean It is well known that an engineruns vccole'i` with a rich fuel and airl mixture' than with aleanmix ture. At high altitudes, thenorrnal cooling ap-y paratus of an engine does not'fun'ction as wellfaes at lower altitudes because `of the" lower density and lower specific thermal capacity of the air. Consequently, aircraft engines are usually operated with a rich mixture at` high altitudes so las to providea cooler operating temperature for the engine. ,4 Y 1 l It is therefore an object of the presentinvem tion tov provide. a signal system for use with an aircraft carburetor havinga mixture controller ver, which systemindicates to the pilot whether` or not the mixture control lever is in the proper position for the existing ight conditions.

Another object of the present invention is to provide a signal system responsive to the attitude of an aircraft and to the position of a carburetor mixture" control lever, nfor indicating to the pilot when the mixture control lever is in the wrong position for the flight of the aircraft in its existing'. attitude.

Another object is to provide asignal system responsive to the rate of climb of an aircraft and to the position of a carburetor mixture control lever, for indicating to the pilot when the mixture control lever is in the wrongposition for the flight of the aircraft at its existing rate of climb.

Another object of the present invention is to provide a signal system responsiveto the position of an aircraft carburetor mixture control lever and tov the altitude of the aircraft for indicating to the pilot when the mixture control lever is in an improper position for operation of the aircraft at th'e particular altitude at which it is flying. A further object is to provide, in a carburetor equipped with altitude compensating means, an arrangement .for utilizing that altitude compensating means in a signal system of the type described. Y

Other cbjects` and advantages of the present invention willbecome apparent from a consideration of .the appended specification, claims, and drawings in which Figure 1 represents, somewhat diagrammatically, an aircraft carburetor provided with a signal system built in accordance with the principles of my invention,

Figurez illustrates an improved switching device which may be used in the system of Figure 1, and

Figures 3 and 4 are electrical wiring diagrams showing the circuits of Figures 1 and 2, respectively. I

In Figure 1, there is shown a carburetor body portion I0 thru which air flows from an inlet .II thru` a passage I 2. to an outlet I3. In iiowing thru the passage I2, the air passes a Venturi restrictionM, a throttle I5, and a fuel discharge nozzle I6.Y

`A second air passage connects the inlet II and the. throat `of the Venturi restriction I4. This second air passage may be traced from the inlet I I thru a plurality of impact tubes II, whose open ends project into the inlet I I, a vent ring passage I8 interconnecting the impact tubes I'I, a conduit 20, an expansible lchamber 2| in a fuel regulator unit 22, a restriction 23, an expansible chamber 3 2d in the regulator unit 22, a conduit 25, an expansible chamber 25 in an altitude responsive switch unit generally indicated at 21, a conduit 28, a chamber 30, and a conduit 3i to the throat of Venturi restriction Ui.

A bellows 32 is mounted in the chamber 3%, and operates a valve 33 which controls the now of air from the passage 23 into the chamber 3i). The bellows 32 is preferably filled with nitrogen or other inert temperature responsive fluid, so that the position of valve 3; is determined by the temperature and pressure of the air in the chamber 33, and hence by the density of that air.

The valve 33 restricts the flow of air thru the second passage just described in such a manner that the pressure differential between chambers 2i and 2@ is an accurate measure of the mass of air flowing thru the passage i2. Errors due to 'fixed restriction or jet 63 in the jet system 31 to the conduit 38. Fuel flowing thru the conduit 6l passes thru a Fixed restriction 64 and a second fixed restriction 65 to the conduit 3B. Fuel entering the jet system 31 thru the conduit 62 may also flow thru a restricted passage 66 to the upchanges in the density of the air with altitude and temperature, and also those errors due to the inherent limitations of a metering restriction of the Venturi type, are substantially eliminated by the operation of valve 33. This type of metering error compensation is more completely described and claimed in my co-pending application Serial No. 490,281, filed June 10,1943, now Patent No. 2,393,144, issued January 15, 1946.

The fuel passing thru the carburetor comes from a fuel pump or other source of fuel under pressure (not shown). From this source, the fuel passes thru a conduit 3A, a fuel regulator unit 22, a conduit S5, a mixture control valve 35, a jet system 31, a conduit 38, a pressure regulator valve di), and a conduit 4l to the discharge nozzle l 6.

The fuel regulator unit 22 comprises a housing 42, which is divided by three flexible diaphragms 43, 4d and i5 into four expansible chambers e6, 2l, 2d and il?. The diaphragms t3.. 4G and 45 are interconnected by a valve stem 18, which carries a balanced valvemember 5i) at its lower end. A compression spring 5l biases the stem 48 for movement of the valve 5i! toward open position. The pressure in chamber l1 is substantially equal to the pressure existing on the upstream side of the jet system 3l. Chamber 136 is connected thru a conduit 52 to an expansible chamber 53 in the pressure regulator 4G. Therefore the pressure in chamber i6 is substantially equal to that existing on the downstream side of the jet system 31. rEhe differential between these pressures is a measure of the quantity of fuel flowing thru the carburetor. This pressure differential is transmitted to the chambers lll and 15, as described above, where it acts on the valve 5i) in a closing direction. As previously pointed out, the pressure differential between chambers 2l and 2&1 is a measure of the mass of air ilowing thru the passage i2, and acts on the valve 50 in an opening direction. Therefore, the valve 5U is operated to proportion the quantity of fuel flowing thru the carburetor in accordance with the mass of air passing thru the passage I2.

The mixture control valve 35 includes a casing 54 forming a generally cylindrical chamber having an inlet port 55 and outlet ports 56 and 51' entering one end of the chamber. A disc valve 58 is fixed in a shaft 6i] which passes axially thru the chamber. The inlet port 55 is connected to the conduit 35. The outlet port 56 is connected by a conduit 6| to the jet system 31, and the outlet por 51 is connected by a conduit -62 to the jet system t1. The shaft Si! may be rotated by a manual control (not shown) so that the disc valve 58 is moved to cover the outlet port 56, or both the outlet ports 55 and 51. When the mixture control stream side of the restriction 65. The passage 66 is normally closed by a spring loaded valve 61, which is adapted to open when the pressure differential across it exceeds a predetermined value. By the operation of the valve S1, the fuel and air mixture supplied to the engine is automatically enriched when the power requirements of the engine are high. An idle valve B9, which may be operated thru linkage not shown, in accordance with changes in throttle position, is provided to control the fuel now when the engine is idling. Under such conditions, the air flow is so small that the controlling effect of the pressure differential between chambers 2| and 24 is overcome by spring 5|, which moves valve 50 toward open position. vIn effect, at low air flows, control of the fuel ow is transferred from the air flow responsive regulator unit 22 to the throttle operated idle valve 59. This is done because at small air flows. the regulating effect of the air now rcsponsive regulator unit is unstable.

The pressure regulator unit 40 includes a casing 1B divided by a diaphragm 'H into a pair of expansible chambers 12 and 53. The diaphragm 1l carries a valve 13 which controls the flow of fuel between the chamber 53 and the conduit 4| A conduit 14 connects the chamber 12 with the conduit 20, and thru conduit ZB, vent ringr I8 and the impact tubes l1 to the air inlet l I. The conduit'M is provided as a vent for the chamber 12 to permit easy movement of the diaphragm 1|. A spring 15 biases the valve 13 for movement toward open position. The pressure in chamber 12 is low compared to the pressure in chamber 53 and the force of the spring 15, so that the pressure in chamber 12 has substantially no controlling effect on the position of valve 13. The valve 13 therefore functions primarily as a pressure regulator to maintain a substantially constant pressure on the discharge side of the jet system 31.

From the foregoing, it will be seen that when the mixture control is in the rich position shown in full lines in the drawings, fuel is supplied to both restrictions 63 and B4. On the other hand, when the mixture control is in the lean position shown in dotted lines in the drawings, fuel is supplied only thru the restriction 63. In either position of the mixture control, the valve 61 may open when the power requirements of the engine are high to further enrich the fuel and air mixture.

Signal system A switch arm is attached to the shaft 6U and insulatingly carries at its end a movable contact 19 which cooperates with a pair of stationary contacts 3l and 82. When the mixture control is in the rich position, the contact 19 engages contact 82. When the mixture control is in the lean position the contact 19 engages contact 8|.

A gravity responsive switch mechanism is shown at 83. In this mechanism, a pendulum 84 is provided with a pair `of movable contacts 85 and 86 which cooperate. respectively with stationary contacts 81 and 88. The pendulum 84 is so arranged that contact 85 engages contact 8l' whenever the aircraft is in level ilight or diving, while the contact 8S engages contact 88 whenever the aircraft is climbing. While a gravity responsive switch is illustrated, it will be readily understood that this may be replaced by a gyroscope or other device which operates a switch in accordance the attitude of the aircraft.

The altitude responsive switch 21 includes a casing 90 divided by a exible diaphragm 9| into a pair of expansible chambers 26 and 92. The central portion of diaphragm 9| insulatingly carries bridging contacts 93 and 94 on its opposite sides. The bridging contact 93 is adapted to engage and electrically connect a pair of stationary contacts 95 and 96, and the bridging contacter@ is adapted to electrically connect a pair of stationary contacts 91 and 98. A compression spring |69 biases the diaphragm 9| for movement to the left.

The chamber 92 is connected thru a conduit lili to the chamber 30. As previously described, the chamber 26 is connected thru conduit 28 and valve 33 to chamber 38. Therefore the pressure differential between the chambers 26 and 92 is the same `as that existing across the valve 33. Since the valve 33 is operated by the bellows 32 toward ated below a rst predetermined altitude, and to f move the bridging contact 94 into engagement with contacts 91 and 98 whenever the aircraft is operating above a second predetermined altitude.

The switch unit 21 also responds to air flow, i e., to the quantity of air flowing thru the passage l2. When the air flow increases, the pressure differential across valve 33 increases, for a given setting of that valve. Therefore it may be seen that, for any given altitude, the switch unit 21 closes its contacts at some particular value of air iiow, depending on the characteristics of spring |90. Furthermore, the particular air flow at which theswitcn unit 21 closes its contacts depends upon and varies with altitude. Altitude and airflow act cumulatively in the switch unit 21. That is, increase in altitude, which signifies the need for a richer fuel and air mixture, acts in the same direction as an increase in air flow, which likewise signifies the need for a richer fuel and air mixture.

The altitude responsive switch unit 21 and the gravity responsive switch unit 33, together with the switch contact 19 associated' with the mixture control 36, control .the energization of a pair of signals |02 and |93. As indicated schematically in the drawing, the signals |02 and |03 may be electrically illuminated signals provided with the legends Go to rich and Go to lean respectively. a

When vthe various switch units are in the positions showm in the drawings, the .mixture control is in the rich position and the aircraft is operating in level flight, and above the altitude at which bridging contact 93 engages the stationaryzcontactstr95 tand'il'.a At this. particulaninters mediatealtitude,..the .power requirements of the enginearewsuch that the engine Amay. operate with1eitherza rich or lean mixture. `If the` aircraft. now'decreases its altitude, contact, 93 is moved into engagement with stationary contacts 99 and 96, thereby completing an energizing circuitI for signal |03. This circuit may be traced from the upper terminal of a battery |04 thru aconductor |65, pendulum 84, contacts 85 and S1, conductor |06, contacts 96, 93 and95, a conductorv lill, signal |03, contact 82, contact 19 and a conductor |08 `to the lower terminal `of battery |64. Energization of signal |03 informs upper tcrminalpf -battery |04 thru conductor pendulum gli, contacts 86 and 88, conductors iiland SH, signal |82, contact 8|, switch Contact 'l and conductor |08 to the lower terminal of battery |04. i

If the altitude of the aircraft is above a predetermined value, bridging contact' 9d engages stationary contacts9l and 98, thereby completing an energizing circuit for signal |02 which may be traced from the upper terminal of battery |84 thru conductors |95 and |l2, contacts 91, 94 and conductors H3, and signal |92, contact 8|, switch contact 19, and conductor |98 to the lower terminal of battery |04.

From foregoing, it should be apparent that whenever either of the signals |02 and '|03 is energized, it remains energized until the mixture control is moved to the position whose necessity is indicated by the signal, and that upon such movement of the mixture control the switch arm breaks the circuit to the signal so that it is no longer energized.

Figure 2 There is shown in Figure 2 a switch mechanism whereby a signal system of the type shown vin Figure l may be operated in accordance with the rate of climb` of an aircraft and in accordance with the quantity of air entering the carburetor. The switch mechanism of Figure 2 may be substituted for the switch 93 of Figure 1. It is desirable to have the carburetor mixture control in its rich position when the aircraft is climbing in order` that the engine may operate under the best conditions for producing maximum power without overheating. It has been found that an engine runs cooler for a given power output when it is supplied with a rich mixture than when it is supplied with a lean mixture. Also, the quantity of air entering the carburetor serves as an indication of the amount of power required at any given time. When the air ow is high, the amount of power developed is high. Under such conditions,v the engine should be operated with a rich.J mixture to prevent overheating of the engine.

Referring now to Figure 2, there is shown a generally cylindrical casing |25 suitably attached to aibase |126. Inside the casing there is mounted on the base |26 a bellowsw|21. A spring |28 is compressed between the .bellows |21 andthe base 1.2.6.. .A pairfof giudeamembersll' andiv |31 project from the base |26 and maintain the spring |28 in proper alignment, The exterior of bellows |21 is exposed to atmospheric pressure thru suitable openings |29 in the casing |25. A passage. |32 extends horizontally from the space adjacent the exterior of bellows |21 to a vertical passage |33 which extends upwardly through the base |26 and is concentric with bellows |21. An elongated nozzle |34 connects the passage |33 with the interior of bellows |21. The passage thru nozzle |34 is of a very narrow cross-section, and restricts the flow of air between the exterior and interior of bellows 21.

As long as the aircraft is operated at a constant altitude, theY pressures inside and outside the bellows |21 are equal. As the aircraft changes its altitude, as by climbing for example, the pressure outside the bellows decreases due to the increase in altitude. This change in pressure is not immediately communicated to the interior of bellows |21 because of the restriction in nozzle |34. Therefore, the bellows |21 tends to expand, The force acting to expand the bellows is proportional to the rate of change of the altitude of the aircraft, and the free end of the bellows |21 is positioned in accordance with the rate of change of the altitude of the aircraft.

There is mounted on the upper or free end of the bellows |21 a rod |35. The rod |35 extends thru a bushing |36 mounted in a transverse wall |4I of the housing 25. There is mounted on the upper end of rod |35 a movable switch contact |31, which cooperates with a pair of stationary contacts |38 and |46.

Above the wall |4I, the interior of the casing |25 is hollow and is divided into two expansible chambers |45 and |46 by a flexible diaphragm |42; The diaphragm |42 carries at its center a bushing |43 thru which the rod |35 passes. A spring |44 is held in compression between an internal shoulder on the housing |25 and the diaphragm |42. The spring |44 biases the diaphragm |42 downwardly.

v The chamber |45 under the diaphragm |42 is connected thru a passage |41 to the conduit 26 of Figure 1. The chamber |46 above the diaphragm |42 is connected thru a passage |48 to the conduit 25 of Figure 1. Therefore, as explained in connection with Figure l, a pressure differential exists between chambers |45 and |46 which is proportional to the quantity of air entering the carburetor.

The rod |35 slides freely thru the bushing |43. A spacer |50 is fixed on the rod |35 just under the contact |31. The lower surface of spacer |50 cooperates with the upper surface of bushing |43. The spring |44 is chosen so that these surfaces are in engagement for all normal flight conditions encountered when the air entering the carburetor is greater than under idling conditions. Therefore, the contact |31 is positioned in accordance with the sum of two forces, one whose magnitude indicates the rate of change of altitude of the aircraft, and another whose magnitude indicates the quantity of air entering the en'gine, and hence the power produced by the engine. Both of these forces act upwardly when the conditions to which they respond change in a direction indicative of the need for a richer fuel and air mixture, and downwardly when the conditions indicate the need for a leaner fuel and air mixture.

Mounted n the top of the casing |25 are a pair of switches generally indicated at and |52. The switch |5| includes a stationary contact |53 anda movable contact |54. The movable contact |54 is attached to a leaf spring |55 which extends inwardly from the outer edge of casing |25. The inner end of leaf spring |55 carries a roller |56 having a surface of electrically insulating material. Stationary contact |53 is carried by another leaf spring |49 which extends substantially parallel to spring |55.

Similarly, the switch |52 includes a stationary contact |51 and a movable contact |58. The movable contact |58 is mounted on a leaf spring |66 which extends inwardly from the outer edge of the casing |55 opposite the switch 5| and carries at its inner end a roller |6I, having a surface of electrically insulating material. Stationary contact |51 is carried by a leaf spring |59 which extends parallel to spring |60.

A mixture control shaft |62 is positioned above the rollers |56 and 6|, and carries a mixture control lever |63 having a downwardly extending cam portion |64 adapted to engage the rollers |56 and |6|, depending upon the angular position of the lever |63.

The leaf springs |55 and |66 are self-biased so that the contacts |54 and |58 tend to engage the stationary contacts |53 and |51, respectively. The mixture control lever |63 is shown in full lines in its lean position, wherein the contact |58 is separated from contact |51. When the mixture control lever |63 is in its rich position, shown in dotted lines in the drawings, the contact |54 is separated from contact |53.

Operation of Figure 2 When the mixture control lever |63 is in the position shown in full lines in the drawings, the carburetor supplies the engine Iwith a lean mixture. If the pilot then starts to climb without moving the mixture control lever to the rich position, the expansion of bellows |21 causes contact |31 to move upwardly into engagement with contact |38. This completes an energizing circuit for a signal |65 which is schematically illustrated as an illuminated signal bearing a suitable legend indicating that the mixture control lever |63 should be moved to its rich position. This energizing circuit may be traced from the upper terminal of a battery |66 thru a conductor |61, signal |55, a conductor |68, a multiple plug connector |16, a. conductor |1|, leaf spring |48, contact |53, contact |54, leaf spring |55, a conductor |12, contact |38, contact |31, rod |35, bushing |36, housing |25, a binding post |13, a conductor |14, connector |10, a conductor |15, and ground connections |16 and |11 to the lower terminal of battery |66. As soon as the pilot moves the lever |63 from the lean position to the rich position in accordance with the indication of the signal |65, the energization of signal |65 is discontinued by the separation of contacts |53 and |54. This separation takes place by virtue cfv the movement of cam |64 into engagement with roller |56.

It will be apparent that the same energizing circuit for signal |65 will be completed whenever the quantity of air entering the carburetor exceeds the value required to cause diaphragm |42 to lift rod |35 sufficiently to cause engagement of contacts |31 and |38.

When the mixture control lever |63 is in its dotted line, or rich position, a signal |86 is energized whenever the quantity of air iiowing thru the carburetor falls below a predetermined value, and the rate of change of altitude of the aircraft falls below ar predetermined value. The occurrence of these two conditions causes a down- Ward'movement of rod |35, thereby carrying contact I3l into engagement with MS'. This `completes the energizing circuit for signal ieri, which may be traced from the upper terminal. of battery lee thru conductor it?, signal ISB, a conductor ISI, connector Ili, a conductor |32, leaf spring lrcontact l5?, contact 56, leaf spring Edil, conductor` lcontact 543, contact IS?, rod 35, bushing litt, casing binding post con duct-or ile, connector iii, conductor H5, `and ground connections llt and Ii'i to the lower ter minal of battery liiii. When the mixture control lever H53 is moved to its lean position in response to such a signal, the signali3d is cle-energized by the |separation of contacts and 58.

If preferred, audible or other sensible signals may be used in place of the illuminated signals illustrated.

While Ihave shown and describedL a preferred embodiment of my invention; other modifications thereof will occur to those skilled in the art, and I therefore intend my invention to be limited only by the appended claims.`

Iclaim as my invention: f

l. Signal apparatus, comprising in combination, a carburetor for an internal combustion en- A gine on an aircraft, manually operable control means associated with said carburetor and mov able between a first position wherein said car-n buretor supplies said engine with a rich fuel and air mixture and a second position wherein said carburetor supplies said engine with a lean fuel and air mixture, first double-throw switch means associated with said control means and moved to first and second circuit-closing positions when said control means is moved to its first and second positions, respectively, second double-throw switch means responsive to the altitude of said aircraft and moved to first and second circuitclosing positions when said aircraft reaches predetermined low and high altitudes, respectively, .g

rst electrical signal means for indicating that said manually operable control means should be moved to said second position, a first electrical circuit for energizing said first signal means and including said rst and second switch means in series, said first circuit being closed when both said first and second switch means are in their first circuit-closing positions, second electrical signal means for indicating that said manually operable control means should be moved to said rst position, and a second electrical circuit for energizing said second signal means and including said first and second switch means in series, said second circuit being closed when both said rst and second switch means are in their second circuit-closing positions.

2. Signal apparatus, comprising in combination, a carburetor for an internal combustion engine on an aircraft, manually operable control means associated with said carburetor and movable between a first position wherein said carburetor supplies said engine with a rich fuel and air mixture and a secondV position wherein said carburetor supplies said engine with a lean fuel and air mixture, rst double-throw switch means associated with said control means and moved to first and second circuit-closing positions when said control means is moved toits first and second positions, respectively, second double-throw switch means responsive to the altitude of said aircraft and moved to rst and second circuitclosing positions when said aircraft reaches predetermined low and high altitudes, respectively, third double-throw switch means responsive to the attitude of said aircraft, said third switch nl ne means being in' a rst circuit-closing position when said aircraft is level or diving and moved to a second circuit-closing position when said aircraft is climbing, first electrical signal means for indicating that said manually operable control means should be moved to said second position, a first electrical circuit for energizing said first signal means and including said rst, second, and third switch means in series, said first circuit being closed when all of said first, second, and third switch means are in their first circuitclosing positions, secondelectrical signal means for indicating that said manually operable control means should be moved to said first position, and a second electrical circuit for energizing said second signal means and including said rst switch means in series with said second and third switch means in parallel, said second circuit being closed when said first switch means and either said second or third switch means are in their second circuit-closing positions.

3. Signal apparatus, comprising in combination, a carburetor for an internal combustion engine on an aircraft, means in said carburetor for proportioning the quantity of fuel supplied to the engine in accordance with the quantity of air flowingthru said carburetor, altitude responsive means associated with said carburetor for compensating the action of said proportioning means, manually operable' control means associated with said carburetor and movable'between `a nrst position wherein said carburetor suppliesV said engine with a rich fuel and air mixture and a second position wherein said carburetor supplies said engine with a lean fuel and air mixture, first double-throw switch means associn ated with said control means and moved to first and second circuit-closing positions when said control means is moved to its first and second positions, respectively, second double-throw switch means, means including said altitude responsive means for operating said second switch means to first and second circuit-closing positions when said aircraft reaches predetermined low and high altitudes, respectively, first electrical signal means for indicating that said manually operable control means should be moved to said second position, a rst electrical circuit for energizing said rst signal means and including said first and second switch means in series, said rst circuit being closed when both said first and second switch means are in their first circuit-closing positions, second electrical signal means for in dicating that said manually operable control means should be moved to said first position, and a second electrical circuit for energizing said second signal means and including said rst and second switch means in series, said second circuit being closed when said first switch means and said second switch means are in their second circuit-closing positions.

4. Signal apparatus, comprising in combination, a carburetor for an internal combustion engine on an aircraft, means in said carburetor for proportioning the quantity of fuel supplied to the engine in accordance with the quantity of air flowing thru said carburetor, altitude responsive means associated with said carburetor for compensating the action of said proportioning means, a manually operable control member associated with said carburetor and movable between a first position wherein said carburetor supplies said engine with a rich fuel and air mixture and a second position wherein said carburetor supplies said engine with a lean fuel and air mixture, a

second member, means including said altitude responsive means for moving said second member between a iirst position corresponding to a predetermined low altitude and a second position corresponding to a predetermined high altitude, signal means operable to indicate the need for a change in position of said control member, and means responsive to the positions of said members to operate said signal means whenever both said members are in their respective rst positions and whenever both members are in their respective second positions.

5. Signal apparatus for an aircraft, comprising in combination, signal means to indicatethe need for a change in the ratio of fuel and air supplied to an internal combustion engine on said aircraft, and means responsive to the resultant of the altitude of said aircraft and the quantity of air flowing to said engine for operating said signal means.

6. Signal apparatus, comprising in combination, a carburetor for an internal combustion engine on an aircraft, manually operable control means associated with said carburetor and movable between a rst position wherein said carburetor supplies said engine with a rich fuel and air mixture and a second position wherein said carburetor supplies said engine with a lean fuel and air mixture, rst double-throw switch means associated with said control means and movable therewith to close first and second pairs of contacts when said control means is moved to its rst and second positions, respectively, a plurality of additional double-throw switch means, each of said additional switch means being responsive to one of a plurality of variable conditions affecting the temperature of said engine and movable to close a rst pair of contacts when its associated condition assumes a value tending to decrease the temperature of said engine and to close a second pair of contacts when its associated condition assumes a value tending to increase the temperature of said engine, rst electrical signal means for indicating that said manually operable control means should be moved to said second position, a first electrical circuit for energizing said first signal means and including all said iirst pairs of contacts in series, second electrical signal means for indicating that said manually operable control means should be moved to said rst position, and a second electrical circuit for energizing said second signal means and including the second pair of contacts on said rst switch means in series with all the second pairs of contacts of said additional switch means in parallel.

'7. `Signal apparatus, comprising in combination, signal means to indicate the need for a change in the ratio of fuel and air supplied to an internal combustion engine, and means responsive to the resultant of the rate of ilow of combustion air to said engine and a condition affecting the temperature of said engine for operating said signal means.

MILTON E. CHANDLER. 

